i 50 Gibson . — Contributions towards a Knowledge 
on the cortical wall. There are two marginal protoxylems 
formed by fusion of the leaf-traces of the dorsal and ventral 
leaves of either side, connected in the young condition by 
procambium, later by metaxylem. A dorsal strand of proto- 
xylem occurs on the stele for some little distance beneath the 
origin of a branch, and is formed by the fusion of the adjacent 
marginal protoxylems of the branch and chief axis. This 
cord soon fuses with the marginal protoxylem of the axis 
beneath on the same side as that on which the branch arises 
(PL IX, Fig. 1). 
The stem is covered externally by a cuticle and epi- 
dermis, followed by a cortex composed outwardly of elongated 
sclerotic fibres, medianly of long thin-walled cells, polyhedral 
in section. The inner cortex consists of smaller cells with 
minute intercellular spaces in which a deposit of silica occurs. 
As I have described this siliceous incrustation in this and other 
species in a previous number of this journal ( 28 ) I need not do 
more than simply indicate its presence. 
The lacuna is large and well defined, and is crossed by 
trabeculae of two types. The first and simpler type consists 
of an endodermal cell with a cuticular band, articulating on 
the cortical side with two swollen cells which arise from 
adjacent cells of the inner cortex. The other type of trabecula 
is derived from this by the swollen cortical cells undergoing 
subdivision, so that the endodermal cell articulates with 
a cluster of cortical cells. These cells contain chlorophyll 
and have a siliceous deposit in the spaces which occur between 
them. I have endeavoured to trace the origin of the cuti- 
cular band on the endodermal cell, and the conclusions I 
have arrived at are somewhat different from the views 
expressed by Hegelmaier, Treub, and others. According to 
the accepted account the cuticular band is local in origin. 
A priori it is somewhat difficult to see why it should be so, 
and more especially when the position of the band in the 
young state is compared with that in the old. It should also 
be borne in mind that if the views of Vladescu and Strasburger 
be correct with regard to the homologies of these cells, viz. 
